Preferred chewing side-dependent two-point discrimination and cortical activation pattern of tactile tongue sensation.

Although tactile feedback from the tongue should contribute to habitual chewing, it is unclear how the sensation of the tongue and its projection to the central nervous system differ with regard to the preferred chewing side (PCS). The purpose of this study was to investigate (1) whether the sensory threshold of the tongue differed according to the side and (2) whether the pattern of hemispheric cortical activation by tactile tongue stimulation differed, with special attention to the PCS. Twelve healthy adults participated in the study. The PCS was determined with a mandibular kinesiograph. In the behavioral study, the mean thresholds for two-point discrimination (TPD) in the anterior, canine and posterior regions on both sides of the tongue, and those between PCS and non-PCS in each region were statistically compared. In the functional magnetic resonance imaging study, tactile stimulation was delivered to either side of the tongue with acrylic balls via a mandibular splint. The runs were measured with a T2*-weighted gradient echo-type echo planar imaging sequence in a 1.5T scanner. Activated voxel numbers in the bilateral primary somatosensory cortex (S1) were statistically compared. The threshold of TPD increased in the order of the anterior, canine and posterior regions. Moreover, this threshold was significantly smaller on the PCS than on the non-PCS in both the canine and posterior regions. Moreover, the number of activated voxels in S1 contralateral to the PCS was significantly greater than that in S1 contralateral to the non-PCS. The present study shows that the PCS is associated with asymmetric tactile sensation and cortical activation of the tongue. The sensory acuity of the tongue on the PCS may play an important role in functional coupling between the jaw and tongue to maximize the efficiency of chewing.